HVOF coating of welded surfaces: Fatigue and corrosion behaviour of stainless steel coated with Inconel-625 alloy

A variety of metallic coatings, produced via the high velocity oxygen fuel (HVOF) process, are available to protect metallic surfaces from high temperature, wear and corrosive environments. Investigation into corrosion and fatigue properties of HVOF coatings is important as they affect the parameters of coated surfaces in their practical applications. In this study, the fatigue behaviour of welded and plain stainless steel surfaces thermally coated with HVOF sprayed Inconel-625 alloy was evaluated under three conditions: (a) surface as-coated, (b) surface as-coated and subjected to aqueous static corrosion for 2 weeks and (c) surface as-coated and subjected to aqueous static corrosion for 4 weeks. The surface morphology and the elemental composition of the coating before and after the fatigue-corrosion test were examined using SEM and EDS techniques. The results indicated that the welded-coated specimen under the three different conditions exhibited a similar fatigue life compared to the plain-coated specimen. However, there was a considerable reduction in the fatigue strength of the coating when subjected to 4 weeks aqueous corrosion medium. Microscopic observations of the fracture surfaces showed that the fatigue cracks were formed at both the interface between coating and substrate, and within the coating itself.